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MAJOR SOIL PROFILES AND THEIR RELATIONSHIP WITH CLIMATE

THE DEPTH TO WHICH CLIMATE AND ORGANISMS EXERT THEIR COMBINED EFFECTS ON THE EARTHY MATERIALS IS THE SOIL PROFILE. IT MAY BE JUST A FEW INCHES DEEP, OR IT MAY BE MANY FEET DEEP. IT CONSISTS OF TWO OR MORE LAYERS, TECHNICALLY CALLED HORIZONS, THAT USUALLY DIFFER FROM EACH OTHER IN SEVERAL CHARACTERISTICS. BELOW IT, IN MOST PLACES, LIES PARENT MATERIAL, THE GEOLOGICALLY WEATHERED EARTHY MATERIAL, YET UNALTERED BY THE COMBINED DYNAMIC FORCES OF CLIMATE AND ORGANISMS. SELECTED SOIL PROFILES FROM DIFFERENT CLIMATES ARE DISCUSSED. TUNDRA SOILS DEVELOPED UNDER FRIGID CLIMATES WITH LOW PRECIPITATION. THEIR PROFILES ARE RELATIVELY SHALLOW, TEND TO BE HIGH IN SILT, LOW IN CLAY, UNIFORM IN TEXTURE WITH PERMAFROST IN THE LOWER PART USUALLY A TOUGH, FIBROUS ORGANIC MAT ON THE SURFACE. PODZOLIC SOILS WERE DEVELOPED UNDER HUMID TEMPERATURE CLIMATES WHERE CHEMICAL AS WELL AS PHYSICAL EFFECTS ARE STRONGLY EXPRESSED. THE SOILS ARE LEACHED AND ACID IN REACTION AND THE CONTRAST IN TEXTURE BETWEEN SURFACE SOIL AND SUBSOIL LAYER IS THE STRONGEST OF ALL GROUPS. ORGANIC MATTER IS PRESENT AS A MAT UP TO SEVERAL INCHES THICK ON TOP OF THE MINERAL SOIL, BUT ITS CONTENT IS LOW WITHIN THE MINERAL SOIL. CHERNOZEMIC SOILS WERE DEVELOPED MAINLY IN SUBHUMID AND SEMIARID, TEMPERATE CLIMATES. THEY SHOW ONLY SLIGHT LEACHING AND LESS TEXTURAL VARIATIONS IN THE PROFILE THAN PODZOLIC SOILS, ALTHOUGH A SIGNIFICANT ACCUMULATION OF CLAY IN THE SUBSOIL IS PRESENT IN MANY. ORGANIC MATTER IS WELL INTEGRATED WITHIN THE MINERAL SOIL THROUGHOUT THE UPPER FOOT OR TWO. DESERTIC SOILS WERE DEVELOPED UNDER ARID CLIMATES, AND THE CLIMATIC EFFECT WAS DOMINANTLY PHYSICAL BREAKDOWN OF PARENT MATERIALS. THEY ARE UNLEACHED AND THEY CONTAIN FREE SALTS. THEY HAVE ONLY SLIGHT TEXTURAL VARIATIONS WITHIN THE PROFILE, BUT CALICHE IN THE SUBSOIL IS A COMMON FEATURE. LATOSOLS WERE DEVELOPED UNDER HUMID AND WET-DRY TROPICAL CLIMATES. THEY SHOW VERY STRONG CHEMICAL AND BIOLOGICAL EFFECTS OF CLIMATE. THEY ARE DEEP, HIGHLY LEACHED, PREVAILING RED IN COLOR, HIGH IN CLAY, LOW IN SILT, FRIABLE AND PERMEABLE. THEY SHOW LITTLE OR NO CLAY ACCUMULATION IN THE SUBSOIL, BUT SHOW A GRADUAL INCREASE IN CLAY CONTENT FROM THE SURFACE DOWNWARD.